This invention relates to a process for producing gasohol, which is a blend of gasoline and ethanol containing approximately 10% by volume ethanol. Ethanol can be readily produced by fermentation processes, which yield dilute aqueous solutions of ethanol. The conversion of such ethanol fermentation beer to substantially anhydrous ethanol for blending with gasoline requires large amounts of heat energy for the required distillations. Ordinary fractional distillation can carry the concentration only to the constant boiling mixture, which is approximately 95 weight percent ethanol. For further concentration, azeotropic distillation is required which involves expensive equipment as well as large amounts of heat energy.
The ultimate role of gasohol in the energy future of the United States and other countries depends on whether its production can be made both energetically and economically appealing. However, to date all published energy and economic analyses for the production of gasohol have been predicated on the assumption that anhydrous ethanol would be produced and subsequently blended with gasoline. Because of the difficulty in obtaining anhydrous ethanol, the separational energy requirement plays a major role in determining the total processing energy, and thus the unfavorable economic outlook for gasohol production.
In considering alternative processes for producing gasohol, some consideration has been given to the possibility of extracting dilute aqueous ethanol with gasoline. See The Colorado Gasohol Task Force Report to the United States Department of Agriculture, dated Jan. 31, 1978, entitled "Production and Marketing of Alcohol Motor Fuels from Colorado Agricultural Commodities: A Tentative Description". However, published phase equilibrium data for ethanol-water-hydrocarbon solvent systems show that the transfer of ethanol is unfavorable in such a process. Further, there is no published data on ethanol-water-gasoline extraction systems, the published data relating only to specific hydrocarbons such as specific aliphatic or aromatic hydrocarbons. See, for example, Nowakowska et al, Ind. Eng. Chem., Data Series, 1, 42 (1956); Vold et al, J. Am. Chem. Soc., 54, 4217 (1932); Washburn et al, J. Am. Chem. Soc., 61, 1694 (1939); and Moulton et al, Ind. Eng. Chem., 45, 2350 (1953).